This invention relates to an apparatus for the manufacture of conical hollow poles with an essentially cylindrical cross-section and made of fiber reinforced synthetic resin, in which the fiber reinforcement is unrolled from a carrying tube inserted into the mold, applied onto the interior wall of the mold and saturated by the synthetic resin which is injected into the mold from one end.
Poles of fiber reinforced synthetic resin are preferably manufactured by centrifugal techniques, that is, a reinforcement of glass fiber or mineral or textile fibers is first made into a conical mold. This mold is placed onto a centrifugal machine by means of carrying rolls and rotated. During rotation, synthetic resin is poured into the mold, completely saturating the reinforcement and forcing it in an outward direction because of the centrifugal force involved and applying it onto the interior walls of the mold. Poles manufactured by this system have proved to be very good. They can be dyed throughout the entire cross-section in various colors and are especially scratch-resistant. They are not susceptible to corrosion and need no care. The material is self-isolating, eliminating the risk of electrical accidents. In traffic accidents when the pole is hit by vehicles, personal and material damages have been found to be much reduced compared to cases involving poles made of steel or concrete.
An important advantage of the centrifugal technique lies in the fact that the reinforcement can be further strengthened at optional places by introducing, for example, one or more additional layers of glass fibers. Such additional reinforcement can be provided wherever a subsequent service door is to be cut out or where additional lights, loud-speakers or the like are to be positioned.
Heretofore, it has been difficult to saturate poles, which were to be provided with additional fiber reinforcement, in such a way that the required wall thickness is present at all places of the pole with the fibers being correctly and completely saturated by the synthetic resin. A filling procedure is known, in which the synthetic resin is poured into the mold from the top and without pressure. Because of the conical shape of the mold, the synthetic resin moves towards the larger cross-section. In another system, a filler channel is introduced into the mold in its longitudinal direction, out of which the synthetic resin flows during the rotation process. The disadvantage of this filling technique is that the fiber reinforcement, being of uneven thickness, cannot be saturated in a reliable fashion.
Attempts have therefore been made to introduce the synthetic resin by a filling lance which is placed into the mold in its longitudinal direction. With the lance enabling a variable, controlled filling, the glass mats can be saturated in a perfect fashion according to their various thicknesses; however, such filling lances have the disadvantage that they are not suitable for molds with a small cross-section and considerable lengths.
A method is further known, in which the entire centrifugal machine is positioned obliquely with the mold, so that the synthetic resin can be distributed in its longitudinal direction and according to the inclination of the mold. This method has the disadvantage that, in the case of high speed of rotation used in modern centrifugal techniques, the resin moves towards the bottom of the pole in spite of the oblique position resulting in a strong resin concentration there. This leads to undesired amounts of resin and larger wall thicknesses at the bottom of the pole which crack during shrinking thus lowering the stability of the product.
Finally, a tempering process for centrifuged synthetic resin poles is part of the modern technique. In this process, either the entire system of the centrifugal machine and mold is placed in a closed container, for example an autoclave, and heated. This results in disproportionately high costs. A different tempering method therefore provides for the removal of the pole from the mold following pre-polymerization of the synthetic resins and for its subsequent hardening in a special oven. Both tempering methods are relatively costly and it is difficult to remove the harmful vapors which occur during the polymerization process.
Accordingly, it is an object of the present invention to manufacture a pole in which fiber reinforcement, having various thicknesses and spread according to static or dynamic needs, can be perfectly saturated by synthetic resin and in which the danger of crack formations at the bottom end is eliminated by appropriate measures. In this connection, it is an object of the invention to assure a perfect tempering and hardening of the pole by technically uncomplicated means and to remove the harmful vapors from the production area.
These objects are achieved, according to the invention, by an apparatus of the initially described type in which the nozzle with the injection stream is guided approximately in the longitudinal direction of the mold and a light source is arranged at the opposite end of the mold illuminating the interior of the mold and a ring flange is fastened to the bottom end of the mold, the interior diameter of which corresponds to the predetermined interior diameter of the pole at the pole bottom.
In this method, the reinforcement is introduced into the mold via a carrying tube. This, in itself, is already known. One or several fiber mats are wound onto a carrying roll. In order to achieve a high bending resilience, the direction of the fibers are preferably oriented longitudinally. In the areas of the desired reinforcements, one or several additional layers of fiber mats are rolled on. The carrying tube with the wound on fiber reinforcement is disposed in the mold. Following a short rotation of the mold, the fiber reinforcement unrolls and attaches itself to the interior wall of the mold. Thereafter, the synthetic resin is injected by spraying from either the bottom or top end of the pole with a free, almost straight jet in the longitudinal direction of the mold.
By changing the angle of spraying of the nozzle, the predetermined amount of synthetic resin can be exactly injected onto the fiber reinforcement in such a way that the glass fiber layers are saturated correctly according to their various thicknesses and in the desired fashion. The injection procedure can be carefully controlled by the light source on the opposite side of the mold so that undesired resin concentrations or insufficiently saturated areas of the reinforcement mats can be eliminated.
Because of the conicity of the form, the resin has a tendency to move away towards the larger diameter during rotation. By the use of a flange which is secured in front of the end of the mold, the synthetic resin is prevented from flowing out in an undesired fashion. The interior diameter of the flange corresponds to the predetermined diameter of the pole. Thus, additional flow of resin cannot collect and form cracks during polymerization.
Further embodiments of the invention have shown that it is especially advantageous if the arrangement is designed in such a way that that end of the form which carries the ring flange is surrounded by a housing in order to catch superfluous synthetic resin. This interception housing has a lateral lower drainage opening for the carrying off of the superfluous synthetic resin from the mold. By a similar arrangement it can be ascertained that the resin is carried back to the production process.
In another embodiment of the invention, the interception housing has an almost central opening for the connection to a heat blower directed towards the interior of the mold.
Following the injection, the polymerization of the pole is initiated by supplying heat. Radiation heat from the outside is used, for example, by using ceramic heating elements. By means of this outside heating element the mold can be preheated prior to the injection process. Additionally, the interior of the rotating mold is heated. This is done by a heat blower blowing warm air into the interior of the pole in an axial direction. This double heating from both the inside and outside results in a very short cycle time without the need for additional hardening devices. This heating technique furthermore promotes the shrinking of the conical pole which takes place during polymerization, and thus provides for easy removal from the mold in the longitudinal direction.
The invention finally provides for a suction housing positioned at one end of the mold surrounding the mold opening and connected to an exhaustor. It is preferable if this suction housing is positioned on the end of the mold having the smaller diameter. By means of the suction exhaustor the harmful vapors produced during polymerization can be reliably removed.
Other features which are considered characteristic of the invention are set forth in the appended claims.
Although the invention is illustrated and described in relationship to specific embodiments, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.